1. Field of the Invention
The present invention relates to photosensitive members having incorporated therein an organic compound of low molecular weight, and more particularly to photosensitive members containing a styryl compound.
2. Description of the Prior Art
Electrophotographic processes generally known include the direct process, the powder image transfer process and the latent image transfer process. With the direct process, the surface of the photosensitive layer of a photosensitive member is charged and exposed to form an electrostatic latent image, which is then developed with developer to a toner image. The toner image is thereafter directly fixed to the photosensitive member to obtain a copy image. In the powder image transfer process, on the other hand, the toner image formed on the photosensitive member is transferred onto a transfer material such as paper and then fixed to obtain a copy image. With the latent image transfer process, the latent image formed on the photosensitive member is transferred onto transfer paper, and the latent image on the paper is then developed and fixed.
Conventional photoconductive materials for forming the photosensitive layer of photosensitive members for use in the electrophotographic processes of the above-mentioned type are inorganic photoconductive materials such as Se, CdS, ZnO and the like. These photoconductive materials have many advantages. For example, they are chargeable to a suitable potential in the dark, are less prone to the dissipation of charges in the dark and permit rapid dissipation of charges when irradiated with light. Nevertheless, these materials have various drawbacks. For example, photosensitive members of Se are costly to make and susceptible to thermal or mechanical shock and must therefore be handled with care. Photosensitive members of CdS or ZnO fail to exhibit stable sensitivity under high-humidity conditions and fail to retain stable characteristics for a prolonged period of time since the pigment incorporated therein as a sensitizer deteriorates owing to corona charging or undergoes discoloration due to exposure to light.
On the other hand, various organic photosensitive polymers inclusive of polyvinyl carbazole have been proposed. These polymers are superior to the above-mentioned inorganic photoconductive materials in film forming ability and lightweightness but are still inferior in sensitivity, durability and stability to changes in environmental conditions.
Organic photoconductive compounds of low molecular weight are preferable in that the properties or electrophotographic characteristics of the film to be formed are controllable by suitably selecting the kind and amount of binder to be used therewith, whereas these compounds must be highly compatible with the binder to be used in combination therewith.
Photosensitive members prepared from a dispersion of such an organic photoconductive compound of high or low molecular weight in a binder resin have the drawback of a high residual potential and low sensitivity due to the presence of many carrier traps. Accordingly, it has been proposed to overcome this drawback by using a charge carrier material in combination with the organic photoconductive material.
While many organic compounds have been proposed as charge carrier materials, the proposed compounds have various actual problems. For example, 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole disclosed in U.S. Pat. No. 3,189,447 has low compatibility with binders and is liable to separate out in the form of crystals. The diarylalkane derivative mentioned in U.S. Pat. No. 3,820,989 has good compatibility with binders, whereas the photosensitive member incorporating the derivative undergoes variations in sensitivity when repeatedly used. Unexamined Japanese Patent Publication No. SHO 54-59143 discloses hydrazone compounds which, although assuring relatively satisfactory initial sensitivity and residual potential characteristics, have the drawback that the sensitivity reduces when the photosensitive member is used repeatedly, hence low durability.